Pneumonia is the world’s leading death among children. Recent findings suggest thatexposure to outdoor air pollutants may increase the risk of pneumonia. The effects of outdoor air pollutantsand the episodes on childhood pneumonia were investigated. A standardized questionnaire on health, homeand environmental factors was conducted for 4988 children in the city of Changsha, and the concentrationof air pollutants including PM10, sulfur dioxide (SO2) and nitrogen dioxide (NO2) during 2008-2011 wasmonitored. Results indicated that the prevalence of pneumonia in children aged 3-6 was 38.21％.Furthermore, the prevalence of children’s pneumonia was significantly positively correlated with both NO2concentration and its episode day, but not with PM10 or SO2. We conclude that exposure to traffic-relatedpollutant may play an important role in the development of childhood pneumonia, and the current nationalambient air pollution standard for NO2 is not reasonable in China.